Resonant oscillating circuits with resonant frequencies (RF) in the megahertz range are increasingly used for electronic theft protection. The primary field of use is in retail sales. Typically, they are made in the form of hang tabs or labels and are connected by machine or manually to the articles to be secured. Increasingly, however, so-called source integration is used; that is, the anti-theft device is already integrated with the article or its package during the production or packaging process.
European Patent Disclosure EP 0 665 705 A2 has already disclosed an RF anti-theft device, which comprises two conductive, spiral windings (spirals). The two spirals are separated from one another by a dielectric layer and are arranged such that they overlap at least partially.
Such resonant frequency anti-theft devices are highly flexible. Since they are moreover quite thin and flat, they can easily be provided with the desired imprint in printers. This imprint is used either for customer information or involves machine-readable information, preferably a bar code.
Bar codes are an economical solution, if the problem is to furnish machine-readable information. It is disadvantageous, in that a bar code must always be placed in the immediate vicinity of the bar code reader, due to optical principles, so that the bar code can be identified. Moreover, the bar code reader can decipher the information only if the bar code is freely accessible or in other words not concealed. The use of a source-integrated anti-theft device with a bar code will therefore make sense--if at all--only in exceptional cases.